In recent years, particularly at hospitals, care sites or the like, there has been increased a demand to comfortably view an image display device such as a liquid crystal display in a position lying on a bed or in a futon, or in a position sitting in a wheelchair or the like. As a device that responds to the above-described demand, for example, as disclosed in JP 2005-84671 A (Patent Literature 1), a retention device to retain the image display device as a viewing object vertically above a lying viewer has been conventionally developed.